In certain applications, such as in the automotive industry, heat exchangers are used to cool or heat certain fluids, such as engine oil or transmission fluid or oil. In the case of transmission fluid, for instance, a heat exchanger is used to cool the transmission fluid. The heat exchanger is usually located remote from the transmission and receives hot transmission oil from the transmission through supply tubing, cools it, and delivers it back to the transmission again through return tubing. However, when the transmission is cold, such as at start-up conditions, the transmission oil is very viscous and does not flow easily through the heat exchanger, if at all. In such cases, the transmission can be starved of oil and this may cause damage or at the least erratic performance. Cumulative damage to the transmission can also occur if the quantity of oil returned is adequate, but is overcooled due to low ambient temperatures. In this case, for instance, moisture condensation in the oil (that would otherwise be vaporized at higher temperatures) may accumulate and cause corrosion damage or oil degradation.
In order to overcome the cold flow starvation problem, various solutions have been proposed in the past. One solution is to use a by-pass path between the heat exchanger supply and return lines often with a heat-actuated by-pass valve located in the by-pass path. There have been short-comings with many prior solutions, including for example, excessive leakage across the valve, sticking of the valve, heat transfer inefficiencies, and/or high cost.
A by-pass valve configuration that addresses many of the short comings of prior actuator valves is shown in U.S. Pat. No. 6,253,837.
However a by-pass valve having additional cost savings, space savings, weight savings and/or operational efficiencies is desirable for some applications.